Mobility

Rolling

What is mobility? Understanding wheeled and traced

mobility How do I control the motors How do I steer How do I know how far I have gone

Mobility: Directed movement of and agent Characteristics (land)

Max height of traversable step, Max width of traversable ditch, Max speed on flat floor, Max traversable slpe, Type of terrain traversable

Cement grave, grass, loose sand etc

Characteristic

Wheeled Tracked Winner

Assuming 20 mph

Complexity •Tire Pressure•Alignment

•Tension•Alignment•Breaking•Weight

Wheeled

Hard Ground• road

Power Required on Hard Ground

3HP/ton 7HP/Ton Wheeled

Power Required on Soft Ground

15HP/ton 10HP/ton Tracked

Soft Ground10 inch layer plastics soild

Reduction in speed on soft or uneven ground if power constant

75-85% 50-75% Tracked

There are several areas of concern Simplicity vs. complexity Reliability Theoretical vs. practical concerns Can I get the parts? Is there a backup plan?

We have already seen the advantages of differentially steered wheels

Using a steering wheel allows one drive motor for

Toy servos often come with a circuit board which can be modified to steer “left”, “centre” and “right”.

Attach servo to “tiller” arm of steering wheel.

Vehicle Weight Movement causes redistribution

Yaw and Slip Yaw caused by turning wheel

side ways, slip caused by loss of friction with surface

Torque Caused by Power to axle

Forward/Reverse Caused by turning of axle due to

torque and momentum of vehicle

Yaw of steered wheels affects grip of wheels on surface

Slip Caused by friction loss between steered wheels and

surface Vehicle will not make a “true”

turn Can be reduced

(sometimes) by adding weight over steering components

Turning radius is quite wide needing lots of real estate

“Actual” turn footprint depends on weight distribution and slip

Slip will be different on all contacting wheels

“Actual” foot print can be reduced by bringing wheels closer together

Uptake hauls track up

Dispersed Weight done by virtue of

track pressure Slip

Caused by friction loss

Top Good Traction and Stability Relatively poor turning

radius Bottom

Reverse characteristics of top arrangement